Processing of optically effective surfaces of spectacle lenses by material removal can be roughly divided into two processing phases, namely initially preparatory processing of the optically effective surface for producing the macrogeometry in accordance with prescription and then fine processing of the optically effective surface in order to eliminate preparatory processing tracks and obtain the desired microgeometry true to shape. Whereas preparatory processing of the optically effective surfaces of spectacle lens is carried out in dependence on, inter alia, the material of the spectacle lenses by grinding, milling and/or turning, in fine processing the optically effective surfaces of spectacle lenses are usually subjected to a precision-grinding, lapping and/or polishing process.
For this fine processing procedure use is increasingly made in the prior art (see, for example, documents U.S. Pat. Nos. 7,278,908 and 9,089,948 or 8,246,424) of adaptable polishing discs by contrast to rigid shape-matched tools. These polishing discs have a substantially three-part or triple-layered construction, comprising (1) a carrier body or base body, which faces the tool spindle and is comparatively firm or rigid and to which (2) a layer softer relative thereto of a resilient material, for example a foam material layer, is secured, on which rests (3) a grinding or polishing film (polishing medium carrier), which faces the tool, as the active tool component for processing. As a consequence of the resilient deformability of the foam material layer the polishing film can within certain limits adapt in situ to the geometry of the surface to the processed. This is not only in a “static” respect, i.e. from spectacle lens to spectacle lens which are to be processed and which usually differ in the geometry thereof, particularly the surface curvature, but also in a “dynamic” respect, i.e. during the actual processing of a specific spectacle lens, in which a relative movement between the polishing disc and the spectacle lens takes place. The resilience of the foam material layer additionally influences to a substantial degree the removal behavior of the polishing disc during the polishing process.
Spectacle lenses, which are to be polished, are encountered with the most diverse geometries in production according to prescription. In macrogeometric terms the radii of curvature of the optically effective surfaces (spheres or cylinders in the case of approximately toroidal surfaces) of the spectacle lenses even in the standard effective range (0 to approximately 14 diopters) extend from infinity (planar surface) to approximately 35 mm. In the case of, for example, freeform surfaces there are to be added still further, more microgeometrically influencing factors such as addition or asphericity. In order to cover the standard effective range, geometrically different polishing disc types which differ, in particular, in the (pre-) curvature of the tool surface active for processing are therefore needed in the above prior art.
Thus, known polishing tool concepts in production according to prescription comprise, for example, seven geometrically different polishing disc types. This obviously obliges, during production of spectacle lenses, a tool change if it is necessary to process successive spectacle lenses differing from one another in their geometry in such a way that they cannot be polished by one and the same polishing disc. However, each tool change is at the cost of productivity in production according to prescription.
Polishing tool concepts for spectacle lens production are also known in the prior art which manage with up to at least three different polishing tool types to cover the standard effective range. Such polishing tools are shown in, for example, document U.S. Pat. No. 7,559,829 B2. In that case, inserted between a foam material layer on which a polishing film rests and a rigid base body by way of which the polishing tool can be held in or at a tool mount is a resilient support structure which comprises a star-shaped part with a plurality of spring arms acting in the manner of a leaf spring and a resilient ring for supporting the spring arms relative to the base body. However, a tool change is similarly necessary in this prior art if spectacle lenses to be polished in succession significantly differ from one another in their geometry. In addition, these polishing tools have a relative complex construction.
What is desired as an improvement over the prior art as represented by document U.S. Pat. No. 8,246,424 is a polishing disc, which is of simplest possible construction, for a tool for fine processing of optically effective surfaces at spectacle lenses, which enables increase in productivity in production according to prescription.